Risk of Later Cancer Small but Real for CT Scans in Kids

Children who had CT scans of the head had a small but increased risk of later leukemia and brain cancer, researchers reported.

by Michael Smith Michael Smith North American Correspondent, MedPage Today
June 06, 2012

Action Points

CT scans of the head in children lead to an increased risk of later leukemia and brain cancer.

Point out that the cumulative absolute risks remain small because both cancers are rare, and is outweighed by the clinical benefit of the scanning, according to the researchers.

Children who had CT scans of the head had a small but increased risk of later leukemia and brain cancer, researchers reported.

But the risk increase is small and is outweighed by the clinical benefit of the scanning, according to Mark Pearce, PhD, of Newcastle University in Newcastle upon Tyne in England, and colleagues.

Nonetheless, CT radiation doses to the head need to be kept low and each use should be justified clinically, Pearce and colleagues argued online in The Lancet.

In a media briefing in London, the researchers took pains to emphasize the clinical value of computed tomography (CT) scans.

"CT scans save lives," said pediatric radiologist Kieran McHugh, FRCR, of Great Ormond Street Hospital for Children in London. He added that modern CT equipment has reduced the dose of radiation by 80% to 90%, compared with machines used before 2002.

The findings, from a large retrospective analysis of more than 178,000 children given CT scans from 1985 to 2002, are the latest entry in a long-running debate.

But, Pearce told reporters, previous studies have used modeling techniques, while the current analysis is "the first direct study of cancer risk in patients who have undergone a CT scan."

The analysis "reduces the debates about whether risks from CT are real," commented Andrew Einstein, MD, of Columbia University Medical Center in New York City.

But awareness of the risks has been increasing and "the specialty has anyway changed strikingly in the past decade, even while the risk debate continued," Einstein said in a commentary accompanying the study.

That awareness will "surely be bolstered by Pearce and colleagues' study," he added.

Also, he noted, at least a dozen other cohort studies are expected to report on the issue, from various countries, in the next few years, which will add to the evidence.

"Pearce and colleagues confirm that CT scans almost certainly produce a small cancer risk," Einstein concluded. "Use of CT scans continues to rise, generally with good clinical reasons, so we must redouble our efforts to justify and optimize every CT scan."

The researchers used British health records to identify children who had been given CT scans, excluding those who were scanned because they already had cancer.

In order to avoid possible confounding, they also excluded patients whose leukemia was diagnosed within two years of their last CT scan and those whose brain tumors appeared within five years of their last scan.

All told, 74 of 178,604 patients were later diagnosed with leukemia and 135 of 176,587 patients developed brain tumors.

Statistical analysis showed that CT radiation was associated with an increased risk of both leukemia and brain cancer. Specifically, the excess relative risk per mGy of radiation was:

0.036 for leukemia, with a 95% confidence interval from 0.005 to 0.12, which was significant at P=0.0097

0.023 for brain tumors, with a 95% confidence interval from 0.010 to 0.049, which was significant at P<0.0001

Among patients who got a cumulative dose of at least 30 mGy, the relative risk of leukemia was more than tripled compared with those whose total dose was less than 5 mGy, Pearce and colleagues reported.

And patients who got a cumulative dose of 50 to 74 mGy had a relative risk of brain cancer that was slightly less than three times the risk seen in those whose total dose was less than 5 mGy.

But the cumulative absolute risks remain small because both cancers are rare, the researchers concluded.

For patients younger than 10, they reported, there is likely to be one excess case of leukemia and one excess case of brain cancer for every 10,000 head CT scans.

Nonetheless, they argued, further reduction in CT dose levels should be a "priority, not only for the radiology community, but also for manufacturers." And other imaging techniques that don't use ionizing radiation, such as ultrasound and magnetic resonance imaging, should be employed where possible.

"Where CT is used," Pearce told reporters, "it should only be used if it can be justified from a clinical perspective."

The study was supported by the National Cancer Institute and the UK Department of Health. The auhtors declared they had no conflicts.

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